Was previously using WP Super Cache but been recently having issues with large traffic on my site so I want to try out W3 Total Cache. Asked my hosting provider to install Memcache on my server and when I tried installing W3 Total Cache, I got these errors:

Page caching is not working properly. Memcached server(s): localhost:11211 may not running or not responding. This error message will automatically disappear once the issue is resolved.

Minify is not working properly. Memcached server(s): localhost:11211may not running or not responding. This error message will automatically disappear once the issue is resolved.

Database caching is not working properly. Memcached server(s): localhost:11211 may not running or not responding. This error message will automatically disappear once the issue is successfully resolved.

Just wanna ask how I can find out the right hostname:port / IP:port to use for the plugin? Is there a way to check or do I need to ask my hosting provider for it? Any help would be appreciated. Thanks!

Your hosting provider should have provided it. Keep in mind that unless you have a multiple server configuration memcached is not the best caching method for all cases.

I installed memcached and got this error, too, even though phpinfo() showed it to be running. I fixed it by following the instructions under W3TC's installation tab to properly initialize it. (It's a standalone program rather than an extension like APC.)

I remember reading at some point that memcached would be better than APC for the object caching -- is this true? I don't have multiple servers, but I do have multiple WordPress installations (in a VPS), all running W3TC. I'm using APC for database caching and memcached for object caching.

(I'm not using the other features because I'm not worried about speed so much as CPU and memory usage.)

Revision (bug?): Setting all 4 WP installations to use memcache for object caching cause all but 1 to be blank. I changed 3 to use APC, leaving the busiest one to use memcached. Maybe I should change its database caching to memcached, too?

I remember reading at some point that memcached would be better than APC for the object caching -- is this true?

No idea where you read that, it's not true. All things are relative.

Revision (bug?): Setting all 4 WP installations to use memcache for object caching cause all but 1 to be blank. I changed 3 to use APC, leaving the busiest one to use memcached. Maybe I should change its database caching to memcached, too?

None of the caching engines have been changed significantly in some time, so I don't understand what bug you mean.

Object caching creates lots of slabs in memcached and you could simply be having excessive cache misses or any number of things that are hard to guess without debugging. If you can your best bet is to give each type of cache it's own memcached instance if for some reason you are compelled to use memcached for your case.

Sorry for the confusion: the revision I meant was of my earlier statement of using memcache. Thanks for the reply.